(1) Field of the Invention
This invention relates to valved couplings for high pressure fluids and is particularly, but not exclusively, useful for controlling the discharge of fluid from pressure vessels containing compressed gas at pressures above 200 kilograms per square centimeter.
(2) Prior Art
A number of valved couplings have been proposed for high pressure hydraulic lines and for pneumatic lines. Thus, British Patent Specification No. 1 339 034 discloses a coupling for a hydraulic line in which valves close off flow upon disconnection of the couplings and the valves also may be closed by cam operation. The specification describes a coupling having a cam which rotates about an axis perpendicular to the flow axis of the coupling, the cam having two diametrically opposite recesses one of which controls a ball valve in the flow passage through the coupling and the other of which controls a sleeve which slides in the bore of the coupling and contains a radial passage which can be aligned with a radial passage through the body of the coupling to relieve pressure downstream of the ball valve when the ball valve is closed. In this arrangement the ball valve and the bleed valve are operated by different parts of a single cam but are otherwise independent of one another. In order to prevent leakage when the radial passages are not aligned with one another, it is necessary to provide O-rings in the wall of the bore on each side of the radial passage in the body and such sealing arrangements are quite unsuitable when they are to have a port moving past them and when they are required to operate at very high pressures. The port formed by the outer end of the radial passage in the sleeve will tend to damage one of the O-rings as it passes the O-ring if the O-ring is to be suitable for high pressures. Also, the O-ring will exert considerable frictional resistance on the movement of the sleeve so that it is possible for the sleeve to jam and for no bleeding to occur.
Another type of coupling incorporating means for bleeding the interior of the coupling when the valve in the coupling is closed is described in British Patent Specification Nos. 1 264 890 and 1 212 777. In this type the coupling includes a rotary ball which acts in the manner of a plug valve and revolves within the seats which engage the circumferential surface of the ball. It will be apparent that such radially engaging surfaces cannot provide sealing against high pressures and are quite unsuitable for pressures of the order of 200 kilograms per square centimeter. A further disadvantage of the construction described in these arrangements is that the bleed passage is opened before the main passage is wholly closed so that there will be a considerable loss of fluid each time the valve is operated.